High-Speed Downlink Packet Access (HSDPA) is an enhanced Third Generation (3G) mobile telephony communications protocol in the High-Speed Packet Access (HSPA) family. HSDPA allows Universal Mobile Telecommunications System (UMTS) based networks to achieve higher downlink data speeds and capacity. As compared to UMTS, HSDPA introduces a new transport layer channel referred to as a High-Speed Downlink Shared Channel (HS-DSCH). The HS-DSCH is implemented using three new physical layer channels, namely, a High-Speed Shared Control Channel (HS-SCCH), a High-Speed Dedicated Physical Control Channel (HS-DPCCH), and a High-Speed Physical Downlink Shared Channel (HS-PDSCH). The HS-SCCH is sent two slots ahead of a corresponding data transmission to a User Equipment device (UE) on the HS-DSCH to inform the UE that data will be transmitted to the mobile terminal on the HS-DSCH two slots ahead. The HS-DPCCH carries acknowledgment information and current Channel Quality Indication (CQI) of the mobile terminal. The HS-PDSCH is the channel to which the HS-DSCH transport channel is mapped that carries actual user data.
Like all other types of networks, cellular communications networks implementing HSDPA must support mobility procedures (e.g., cell changes). The mobility procedures are based on the concept that the HS-DSCH allocation for a given UE belongs to only one of the radio cells assigned to the UE, the serving cell for the HS-DSCH or the serving HS-DSCH cell. The HS-DSCH radio link for the UE on the serving HS-DSCH cell is referred to as the serving HS-DSCH radio link. The main purpose of HSDPA mobility procedures is to handle serving HS-DSCH cell changes. When the UE moves between cells, the HSDPA connection is maintained by means of an intra-frequency serving HS-DSCH cell change between the source and target cells, both of which are in an Active Set (AS) of cells for the UE. In general, evaluation for the HS-DSCH cell change is triggered only if the parameter hsCellChangeAllowed (hsCellChangeAllowed is an overall On/Off switch for serving HS-DSCH cell change used by the Radio Network Controller (RNC) to check whether it should proceed with the cell change or not) is set to TRUE. An HS-DSCH cell change is normally triggered by event 1 d HS, that is a change of the best cell for the UE within the AS, but a serving cell change can also be triggered when the current serving cell should be removed from the AS. If Enhanced Uplink (EUL) is supported in the network, the serving cell for the EUL, which is referred to herein as the EUL serving cell, is always the same as the HS-DSCH serving cell, and the cell change is performed for both EUL and HSDPA at the same time.
The mobility procedures are based on the collection of mobility measurements from the UEs. In particular, a number of measurement handling entities for HSDPA operate to collect, control, and store the UE measurements needed for HSDPA mobility procedures and to distribute these measurements to the involved HSDPA mobility procedures, as illustrated in FIG. 1.
HSDPA defines a HS-DSCH cell change procedure whereby the RNC evaluates whether a HS-DSCH cell change should be performed for a particular mobile terminal. The HS-DSCH cell change procedure is illustrated in FIG. 2. As illustrated, a RNC 10 controlling a serving HS-DSCH cell of a UE 12 sends a measurement control message for event 1 d HS to the UE 12 (step 100). When PS Interactive (which refer to interactive class of service using R99 bearers) using either Dedicated Channel (DCH) or HSDPA is started, an extra measurement control message related only to the event 1 d HS is sent to the UE 12. This measurement control message has a measurement Identifier (ID) that is different than the measurement ID of another measurement control message dealing with the conventional event 1 d for soft handover evaluation. The reason for having a separate event 1 d HS is to be able to get UE reports triggered by only AS cells and to be able to use different hysteresis and time to trigger parameters to trigger serving HS-DSCH and EUL cell change. It is also possible to use a different quality criterion than that used for the conventional event 1 d. The default quality criteria used for the event 1 d HS is Common Pilot Channel (CPICH) Received Signal Code Power (RSCP).
The UE 12 performs measurements for the event 1 d HS (i.e., CPICH RSCP measurements on cells in the AS) (step 102). The UE 12 evaluates the measurements (step 104). In particular, when a cell in the AS becomes stronger than the current best cell+hsHysteresis1 d/2 in the AS, during a time at least equal to hsTimeToTrigger1 d, event 1 d HS occurs. The current best cell is the serving HS-DSCH cell. In response to detecting the event 1 d HS, the UE 12 sends a measurement report message for event 1 d HS to the RNC 10 (step 106)
Upon receiving the measurement report message for the event 1 d HS, the RNC 10 performs RNC evaluation to determine whether to attempt to perform a serving HSDPA/HS-DSCH cell change to the new best cell (step 108). If a triggered cell change cannot be performed, then an attempt to reconfigure the connection to DCH is normally made. This will happen for example when the UE 12 leaves an area where HSDPA is supported, or for a Drift Radio Network Controller (DRNC) cell if lur support is not configured.
For RNC evaluation, when a HS-DSCH cell change is triggered by a change of the best cell, that is event 1 d HS, then the RNC 10 performs RNC evaluation as follows. The RNC 10 determines whether the parameter hsCellChangeAllowed is TRUE. If so, the RNC 10 performs a valid target cell evaluation within the current AS. The RNC 10 then selects the best of the AS cells that supports HS-DSCH. The selected best cell of the AS that supports HS-DSCH is HS-DSCH capable and is better than the current serving cell of the UE 12 by hsHysteresis1 d/2. If these conditions are fulfilled, then a suitable cell for the HS-DSCH cell change is found.
If a suitable cell is found, then the RNC 10 will start execution of a HS-DSCH cell change from the current serving cell (i.e., the source cell) to the best/suitable cell (i.e., the target cell). The RNC 10 first performs HS-DSCH radio link setup (step 110). In particular, a radio link reconfiguration is performed to release the HS-PDSCH resources on the HS-DSCH radio link of the source cell (i.e., the current/old serving cell) (Node B Application Part (NBAP) message from the source cell to the Serving RNC (SRNC)) and setup the HS-PDSCH resources on the HS-DSCH radio link of the new/target cell (NBAP message from the SRNC and the target cell on the same or different Node B). If the NBAP radio link reconfiguration is successful (i.e., HS-DSCH link setup is successful), a Radio Resource Control (RRC) physical channel reconfiguration is performed (steps 112-116). Finally the old HS-DSCH resources are released (step 118). At this point, execution of the HS-DSCH cell change is complete. Step 120 implies evaluation of a new Neighbor List, which has to be created after the successful HS-DSCH cell change procedure. The same is then communicated to the UE 12 via a RRC Measurement Control Message (step 122).
Notably, while not illustrated in FIG. 2, if the HS-DSCH cell change cannot be completed, then the RNC 10 will attempt to reconfigure to DCH instead. The HS-DSCH cell change can fail if the parameter hsCellChangeAllowed is FALSE, if no suitable cell for the HS-DSCH cell change is found, or if the cell change execution fails and the connection does not drop. Cell change can fail due to cell change for the EUL being blocked by admission control (if the connection is using a 2 millisecond (ms) Transmission Time Interval (TTI), the connection is reconfigured to a 10 ms TTI EUL and the cell change is re-attempted). The RNC 10 checks the parameter hsToDchTrigger and, if the transition to DCH is allowed, continues with the reconfiguration to DCH. Otherwise, the RNC 10 takes no more actions. If the transition to DCH is blocked by admission control or fails, then the RNC 10 takes no more actions.
The inventors have found that the conventional HS-DSCH cell change procedure described is less than ideal in that, under certain scenarios, the user experience after the cell change may be poor. As such, there is a need for systems and methods for improved HS-DSCH cell change.